The role of fibrocartilage in joint development and disease has received little attention. This tissue contributes only a small amount to the total cartilage on articular surfaces. However, its strategic location suggests a significant role in joint mechanics. Fibrocartilage also occurs in the form of intraarticular disks and menisci. Others have found differences between hyaline and fibrocartilage in histology and ultrastructure of cells and matrix. These findings, and the limited embryological, biochemical, and biomechanical data available, suggest that changes in fibrocartilage have little-recognized key roles in degenerative joint disease and rheumatoid arthritis. Understanding fibrocartilage organization, biochemistry, and biology may underly clarification of some early changes occuring in joint diseases, and thereby underly design on new therapeutic modalities. This project is designed to develop a clearer description of fibrocartilage by: 1) characterizing the proteoglycans and collagen of the extracellular matrix, 2) characterizing the behavior of fibrocartilage and fibrochondrocytes in culture, 3) mapping the distribution of articular fibrocartilage in the knee joint, and 4) characterizing its histology and ultrastructure more fully. Subsequent studies will examine the role of changes in fibrocartilage in experimental models of joint diseases. The rabbit knee is being used in these studies.